In a current user interface system, e.g., a user interface of a portable device like a mobile phone, methods for rendering graphics or images include a 2D image rendering approach and a 3D image rendering approach. The 2D image rendering approach is easier and less expensive to implement, yet has a disadvantage of lacking depth information. The 3D image rendering approach, although having an advantage of being capable of rendering better visual enjoyment to viewers using its depth information, is burdened with more complicated and more costly implementation. More specifically, when the 3D image rendering approach is realized by hardware, corresponding hardware cost is much higher than that of the 2D image rendering approach; when the 3D image rendering approach is realized by software, a processor needs to designate more resources and time in rendering the 3D images such that a processor performance may be significantly degraded due to the 3D image rendering approach.